An Indonesian woman has been sentenced to six months in jail after she documented sexual harassment by her employer.

Baiq Nuril Maknun, 37, who worked at a school on the island of Lombok, recorded a telephone conversation with the headteacher, whom she accused of making repeated unwanted sexual advances, her lawyer Joko Jumadi said. A colleague used the audio to lodge an official complaint against the headteacher.

Indonesia’s supreme court in Jakarta convicted Maknun on Thursday of recording and spreading indecent material under the country’s electronic information and transactions law.

“The supreme court judges were satisfied that she has violated the law,” a court spokesperson told the Thomson Reuters Foundation. The court sentenced Maknun to six months in prison and fined her 500m rupiah (£26,400) after overturning a 2017 acquittal from a lower court.

Amnesty Indonesia’s executive director, Usman Hamid, said: “It appears a woman was criminalised simply for taking steps to redress the abuse she experienced. It is a travesty that while the victim of the alleged abuse has been convicted … little if any action appears to have been taken by the authorities to investigate what appear to be credible claims.”

Maidina Rahmawati, of the Institute for Criminal Justice Reform, a Jakarta-based non-profit organisation, said the ruling could be used to deter other victims from reporting future abuses. “This case is an example of how the law, which is too vague, could be used against vulnerable women who were trying to protect themselves,” she said.

One-third of Indonesian women have faced physical or sexual violence, according to a government survey released last year, prompting calls from campaigners for action.

The court ruling was delivered in a closed-door deliberation on 26 September and only made public this week. Jumadi said they would file for a judicial review to challenge the ruling. “She is a victim and she just wants justice,” the lawyer said.